FIG. 1 illustrates a light emitting diode (hereinafter referred to as ‘LED’) in which quantum well layer is formed as the light emitting layer.
Referring to FIG. 1, the LED includes a substrate 1, and a n-type semiconductor layer 2, a quantum well layer 3 and a p-type semiconductor layer 4, which are laminated in the named order on the substrate 1.
In the LED of FIG. 1, when a forward bias is applied to the LED, electrons are supplied from the n-type semiconductor layer 2 and holes are supplied from the p-type semiconductor layer so that electrons and holes are recombined with each other in the quantum well layer 3. In the course of recombination, the LED emits light with an energy corresponding to excited level of quantum well or energy bandgap difference.
At this time, the quantum well layer 3 serves as the light emitting layer and accordingly shows a high internal quantum efficiency compared with an LED having a double heterojunction structure, but it is the reality that the internal quantum efficiency does not exceed 10%.
To this end, even when the LED is used as a high power LED, it has a drawback in that power consumption is high, a lot of heat is generated and the generated high temperature heat changes the characteristic of the LED to thereby lower the reliability.